Optimizing a file system interface in a virtualized computing environment

ABSTRACT

Systems and methods for optimizing write operations to a storage device in a virtualized computing environment comprise monitoring write operations issued by an application running on a virtual machine&#39;s (VM) operating system, wherein the VM is hosted by a hypervisor providing access to a storage device in a virtualized computing environment; and causing a virtual file system (VFS) supported by the operating system to call on a first para-virtualized file system (PVFS FE) supported by the operating system to execute a write operation, in response to determining that the write operation is to write data to the storage device, wherein data that is to be written to the storage device is first written to a VM memory area allocated to the VM and accessible to the hypervisor hosting the VM.

COPYRIGHT & TRADEMARK NOTICES

A portion of the disclosure of this patent document may containmaterial, which is subject to copyright protection. The owner has noobjection to the facsimile reproduction by any one of the patentdocument or the patent disclosure, as it appears in the Patent andTrademark Office patent file or records, but otherwise reserves allcopyrights whatsoever.

Certain marks referenced herein may be common law or registeredtrademarks of the applicant, the assignee or third parties affiliated orunaffiliated with the applicant or the assignee. Use of these marks isfor providing an enabling disclosure by way of example and shall not beconstrued to exclusively limit the scope of the disclosed subject matterto material associated with such marks.

TECHNICAL FIELD

The disclosed subject matter relates generally to a virtualized filesystem interface and, more particularly, to a system and method foroptimizing data operations over such interface.

BACKGROUND

A virtual machine (VM) is a software implementation of a machine (i.e.,a computer) that executes programs like a physical machine would.Generally, access to resources in virtualized environments is associatedwith a high level of overhead because the VM typically cannot directlycommunicate with a virtualized resource. A hypervisor that hosts the VMtypically has the burden of emulating the needed interface or driver onbehalf of the VM. In other words, the hypervisor presents the VM with avirtual platform and monitors the execution of the VM and how the VMaccesses the available hardware resources.

For example, for a VM to read or write data to a virtualized storagedevice, control of the read or write operations will have to betransferred between the VM and the hypervisor. The hypervisor may useany type of storage interface for storing the VM's data, including localfile system, network file system, network block device, etc. In a purelyemulated case, the VM has no knowledge that the provided interface(i.e., the block device) is not a real physical device, because thehypervisor emulates the interface in software. A high overhead isassociated with such emulation. The operational overhead is even morecostly, if there is a need for transferring control intermittentlybetween the VM and the hypervisor during I/O operations.

SUMMARY

For purposes of summarizing, certain aspects, advantages, and novelfeatures have been described herein. It is to be understood that not allsuch advantages may be achieved in accordance with any one particularembodiment. Thus, the disclosed subject matter may be embodied orcarried out in a manner that achieves or optimizes one advantage orgroup of advantages without achieving all advantages as may be taught orsuggested herein.

In accordance to one embodiment, a method for optimizing writeoperations to a storage device in a virtualized computing environmentcomprises monitoring write operations issued by an application runningon a virtual machine's (VM) operating system, wherein the VM is hostedby a hypervisor providing access to a storage device in a virtualizedcomputing environment; and causing a virtual file system (VFS) supportedby the operating system to call on a first para-virtualized file system(PVFS FE) supported by the operating system to execute a writeoperation, in response to determining that the write operation is towrite data to the storage device, wherein data that is to be written tothe storage device is first written to a VM memory area allocated to theVM and accessible to the hypervisor hosting the VM; wherein a secondpara-virtualized file system (PVFS BE) supported in the hypervisorasynchronously scans the VM memory to determine if any data that hasbeen stored in the VM memory is to be written to the storage device, andwherein the PVFS BE writes the data that is to be written to the storagedevice from VM memory to the storage device.

In accordance with one or more embodiments, a system comprising one ormore logic units is provided. The one or more logic units are configuredto perform the functions and operations associated with theabove-disclosed methods. In yet another embodiment, a computer programproduct comprising a computer readable storage medium having a computerreadable program is provided. The computer readable program whenexecuted on a computer causes the computer to perform the functions andoperations associated with the above-disclosed methods.

One or more of the above-disclosed embodiments in addition to certainalternatives are provided in further detail below with reference to theattached figures. The disclosed subject matter is not, however, limitedto any particular embodiment disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed embodiments may be better understood by referring to thefigures in the attached drawings, as provided below.

FIGS. 1, 2A and 3A illustrate exemplary computing environments inaccordance with one or more embodiments, wherein a VM hosted by ahypervisor is implemented to read from or write to a storage deviceaccessible via the hypervisor.

FIGS. 2B and 3B are exemplary flow diagrams of methods for respectivelyreading or writing to the storage device illustrated FIGS. 1, 2A and 3A,in accordance with one embodiment.

FIGS. 4A and 4B are block diagrams of hardware and software environmentsin which the disclosed systems and methods may operate, in accordancewith one or more embodiments.

Features, elements, and aspects that are referenced by the same numeralsin different figures represent the same, equivalent, or similarfeatures, elements, or aspects, in accordance with one or moreembodiments.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In the following, numerous specific details are set forth to provide athorough description of various embodiments. Certain embodiments may bepracticed without these specific details or with some variations indetail. In some instances, certain features are described in less detailso as not to obscure other aspects. The level of detail associated witheach of the elements or features should not be construed to qualify thenovelty or importance of one feature over the others.

Referring to FIG. 1, in accordance with one embodiment, a VM 105 may behosted by a hypervisor 100, in a computing environment. The hypervisor100 is implemented to emulate an interface (e.g., a block device) toallow the VM 105 communicate with a resource (e.g., storage device 180)that is accessible via the hypervisor 100. Depending on implementation,the overhead associated with the emulation and the need for transfer ofcontrol between VM 105 and a hypervisor 100 may be reduced by way ofusing a para-virtualized block driver in place of a standard driverwhich requires device emulation.

When the VM 105 uses a para-virtualized component (e.g., a block driver)the performance may be optimized by batching multiple I/O requests andusing shared memory to avoid multiple data copies, as provided infurther detail below. As shown in FIG. 1, a computer-implementedapplication such as a software code (e.g., user space application 107)may be running on a VM operating system 109 executed on VM 105. The VMoperating system 109 may support a virtual file system (VFS) 120 and afirst para-virtualized file system (PVFS FE) 140. The hypervisor 100 maysupport a second para-virtualized file system (PVFS BE) 160 capable ofcommunicating with PVFS FE 140.

In one implementation, the PVFS FE 140 and the PVFS BE 160 are utilizedto allow VM 105 to perform read/write operations on storage device 180such that the write operations are performed by way of asynchronouscommunication between VM 105 and hypervisor 100 and the read operationsare performed by way of file system level requests. It is noteworthythat the VM's 105 memory (not shown) is desirably fully accessible fromthe hypervisor 100. In accordance with one embodiment, apara-virtualized file system is implemented differently from a typicalfile system in that the para-virtualized file system is aware that it isrunning in VM 105 and not directly on hardware, and uses the virtualmachine's specific properties to provide additional functionality. Forexample, here the PVFS FE 140 and PVFS BE 160 utilize shared memory toimprove performance A typical file system (e.g., NTFS, ext3) running inVM 105 is agnostic to the fact that it is running in a virtualenvironment.

For example, device assignment option may be utilized to allow the VM105 access storage device 180. A device assignment grants the VM 105,desirably, full access to storage device 180 so that the VM 105 may sendI/O requests directly to storage device 180. Interrupts may be routedthrough the hypervisor 100. Device assignment option may not bedesirable if storage device 180 is intended for sharing among severalVMs and the hypervisor and may not support VM migration due to the VM'sdirect interface assignment to a particular device, instead of thehypervisor provided interface. It is noteworthy that in the following,the term data may refer to either content data or metadata correspondingto such data, or both. In this context, metadata may be data thatprovides additional information about the content data, such asdirectory listings, modes, or indirect blocks, without limitation.

Referring to FIGS. 2A and 2B, in one embodiment, VM user spaceapplication 107 may issue a system call. The VM's operating system 109monitors the system calls for I/O operations (S210) and calls on the VFS120 to determine whether the system call is to be handled by the PVFS FE(S220). If so, the VFS 120 calls on PVFS FE 140 to handle the systemcall, which may be for executing a write operation, for example (S230).It is noteworthy that a write operation may be the result of a metadataupdate system call, or any other operation that results in updating dataor metadata on storage device 180. The data that is to be updated orwritten may be stored in the VM's 105 memory which is accessible fromthe hypervisor 100.

In accordance with one embodiment, since the PVFS FE 140 resides in theVM's operating environment, PVFS FE 140 shares the VM's memory totemporarily cache the data that is to be written to storage device 180.On the other hand, since PVFS BE 160 resides in the hypervisor's 100operating environment, and the hypervisor 100 has access to VM's 105memory, then PVFS BE 160 also has access to VM's 105 memory.

In one implementation, the PVFS BE 160 asynchronously scans the VM's 105memory to determine if any data or metadata that has been stored in thememory needs to be written to storage device 180, and, if so, PVFS BE160 writes that data to storage device 180 (S240). The PVFS BE 160 thenmarks the respective data in the VM's 105 memory to indicate that saiddata has been written to storage device 180 (250). The asynchronousscanning may be performed based on the passage of a time interval fromthe last scan or determining that a certain amount of data has beenwritten to VM's 105 memory or determining that a certain number ofwrites has been performed to the VM's 105 memory by the PVFS FE 140after the last scan.

In certain embodiments, more advanced algorithms for predicting the VM'sbehavior may be utilized to determine the nature and frequency of VM'smemory scans. For example, PVFS BE 160 or other scanning utility maymonitor and model PVFS FE's 140 write patterns to predict when VM memoryshould be scanned. Or recent write history to the storage device 180 maybe used to determine how often the VM's memory should be scanned.

Referring to FIGS. 3A and 3B, in one embodiment, user space applicationin VM 105 may issue a read system call to read data from storage device180. The VM's 105 operating system monitors the system calls (S310) andcalls on the VFS 120 to determine whether a read operation should behandled by the PVFS FE 140 (S320). If so, then the operating systemcauses the VFS 120 to call on PVFS FE 140 to execute the read operation(S330). It is noteworthy that a read operation may be the result of ametadata read system call, or any other operation that results inreading data or metadata on storage device 180.

If the data to be read exists in PVFS FE's 140 cache (S340), then PVFSFE 140 attempts to satisfy the read request from its cache and executesthe read operation (S370). However, if a cache miss is encountered(e.g., if the target data or the corresponding metadata is not in PVFSFE's 140 cache), PVFS FE 140 passes the original read operation to PVFSBE 160 (S350). Desirably, PVFS BE 160 executes the read operation(S360), either entirely from PVFS BE's 160 cache or from the storagedevice 180, if the data or the corresponding metadata are not present inPVFS BE's 160 cache.

In accordance with one embodiment, the PVFS BE 160 returns the memorypages it used to satisfy the request to the PVFS FE 140 so that PVFS FE140 can populate its cache, and so that PVFS FE 140 may return therequested data to the VFS 120. It is noteworthy that in certainimplementations the returned memory pages include the target data or thecorresponding metadata or both.

Accordingly, in one or more embodiments, the hypervisor 100 isconfigured to have access to at least a portion of the VM's 105 memory.To perform certain I/O operations or file system modifications such ascreating a file or writing to a file, the VM 105 modifies its in-memoryfile system state. The in-memory file system state includes data andcorresponding metadata. The metadata may define the file systemstructure or provide additional information about a directory or a filein the file system. The PVFS BE 160 desirably asynchronously monitorsthe VM's 105 in-memory file system state and performs the proper writeoperations to commit the VM's modifications to storage device 180.

As such, in case of a write operation, the interface between PVFS FE 140and PVFS BE 160 is asynchronous implemented, so that the VM 105 won'thave to request for hypervisor 100 to control the write operation on theVM's behalf by way of a fully emulated or para-virtualized I/Ointerface. The PVFS BE's 160 asynchronous monitoring of the VM's 105memory may result in the more efficient use of CPU power in contrast toimplementations that require synchronous monitoring. In someimplementations, the monitoring may be limited to one pass every fewseconds, for example.

To avoid several switches (i.e., control transfers) between hypervisor100 and VM 105 during a data or meta-data read operation, a single filesystem level read operation is utilized to service several disk blockread requests. A single file system level read operation is a high-levelVFS call, which is generally similar to a system call (e.g., readingfrom a file, reading file metadata, listing directory contents, etc.).It is noteworthy that in certain implementations no differentiation ismade between data and metadata reads. To avoid servicing several diskblock requests to read metadata in order to find the target data,followed by several requests to read the target data itself, the PVFS FE140 is implemented to send a file system level request to the PVFS BE160.

The PVFS BE 160, in one embodiment, simulates the read operation todetermine the storage device's 180 segments that the PVFS FE 140 willneed in order to fulfill the PVFS BE 160 read request. The PVFS BE 160may retrieve the necessary segments from its cache or from storagedevice 180, and then transfers the data segments to the VM 105 together,so that the PVFS FE 140 may satisfy the read request from its cache.

The above implementation reduces the number of intermittent controlswitches that may be needed between the VM 105 operating system and thehypervisor 100, if the data segments were to be cached individually. Theelimination of multiple switches improves read performance. In certainexemplary embodiments (e.g., NFSv4), a network file system protocol'scompound operations may be utilized to implement the above configurationwhere a lookup and read request may be transferred from a client to theserver via a single remote procedure call (e.g., RPC). In oneembodiment, the hypervisor 100 provides the VM 105 with the informationVM 105 needs to populate its cache and execute the operation itself.Future VM 105 read operations may thus be satisfied from cache without aneed for a control switch back to the hypervisor 100.

In certain embodiments, the above system may be implemented as apara-virtualized file system in a kernel based virtual machine (KVM)hypervisor. KVM includes a notification based protocol that supports ashared memory mechanism between a VM 105 and a hypervisor 100. For thehypervisor 100 to efficiently track writes that the VM 105 performs tomemory, a para-virtualized file system may be implemented on alog-structured file system (e.g., LFS or NILFS). In such exemplarylog-structured file systems, data and metadata writes are appended to alog.

LFS divides a storage device into segments, wherein one of the segmentsis active at any one time. Each segment has a header called a summaryblock. Each summary block contains a pointer to the next summary block,linking segments into a chain that LFS treats as a linear log. Due tothe nature of the log which supports append-only data writes, forexample, the hypervisor 100 may efficiently detect writes performed byVM 105. For example, if a file meta-data update is necessary, the PVFSFE 140 will append the operation to the log. PVFS BE 160 will thenmonitor the log for new appends instead of monitoring all datastructures of PVFS FE 140 to detect updates.

In different embodiments, the claimed subject matter may be implementedas a combination of both hardware and software elements, oralternatively either entirely in the form of hardware or entirely in theform of software. Further, computing systems and program softwaredisclosed herein may comprise a controlled computing environment thatmay be presented in terms of hardware components or logic code executedto perform methods and processes that achieve the results contemplatedherein. Said methods and processes, when performed by a general purposecomputing system or machine, convert the general purpose machine to aspecific purpose machine.

Referring to FIGS. 4A and 4B, a computing system environment inaccordance with an exemplary embodiment may be composed of a hardwareenvironment 1110 and a software environment 1120. The hardwareenvironment 1110 may comprise logic units, circuits or other machineryand equipments that provide an execution environment for the componentsof software environment 1120. In turn, the software environment 1120 mayprovide the execution instructions, including the underlying operationalsettings and configurations, for the various components of hardwareenvironment 1110.

Referring to FIG. 4A, the application software and logic code disclosedherein may be implemented in the form of computer readable code executedover one or more computing systems represented by the exemplary hardwareenvironment 1110. As illustrated, hardware environment 110 may comprisea processor 1101 coupled to one or more storage elements by way of asystem bus 1100. The storage elements, for example, may comprise localmemory 1102, storage media 1106, cache memory 1104 or othercomputer-usable or computer readable media. Within the context of thisdisclosure, a computer usable or computer readable storage medium mayinclude any recordable article that may be utilized to contain, store,communicate, propagate or transport program code.

A computer readable storage medium may be an electronic, magnetic,optical, electromagnetic, infrared, or semiconductor medium, system,apparatus or device. The computer readable storage medium may also beimplemented in a propagation medium, without limitation, to the extentthat such implementation is deemed statutory subject matter. Examples ofa computer readable storage medium may include a semiconductor orsolid-state memory, magnetic tape, a removable computer diskette, arandom access memory (RAM), a read-only memory (ROM), a rigid magneticdisk, an optical disk, or a carrier wave, where appropriate. Currentexamples of optical disks include compact disk, read only memory(CD-ROM), compact disk read/write (CD-R/W), digital video disk (DVD),high definition video disk (HD-DVD) or Blue-Ray™ disk.

In one embodiment, processor 1101 loads executable code from storagemedia 1106 to local memory 1102. Cache memory 1104 optimizes processingtime by providing temporary storage that helps reduce the number oftimes code is loaded for execution. One or more user interface devices1105 (e.g., keyboard, pointing device, etc.) and a display screen 1107may be coupled to the other elements in the hardware environment 1110either directly or through an intervening I/O controller 1103, forexample. A communication interface unit 1108, such as a network adapter,may be provided to enable the hardware environment 1110 to communicatewith local or remotely located computing systems, printers and storagedevices via intervening private or public networks (e.g., the Internet).Wired or wireless modems and Ethernet cards are a few of the exemplarytypes of network adapters.

It is noteworthy that hardware environment 1110, in certainimplementations, may not include some or all the above components, ormay comprise additional components to provide supplemental functionalityor utility. Depending on the contemplated use and configuration,hardware environment 1110 may be a desktop or a laptop computer, orother computing device optionally embodied in an embedded system such asa set-top box, a personal digital assistant (PDA), a personal mediaplayer, a mobile communication unit (e.g., a wireless phone), or othersimilar hardware platforms that have information processing or datastorage capabilities.

In some embodiments, communication interface 1108 acts as a datacommunication port to provide means of communication with one or morecomputing systems by sending and receiving digital, electrical,electromagnetic or optical signals that carry analog or digital datastreams representing various types of information, including programcode. The communication may be established by way of a local or a remotenetwork, or alternatively by way of transmission over the air or othermedium, including without limitation propagation over a carrier wave.

As provided here, the disclosed software elements that are executed onthe illustrated hardware elements are defined according to logical orfunctional relationships that are exemplary in nature. It should benoted, however, that the respective methods that are implemented by wayof said exemplary software elements may be also encoded in said hardwareelements by way of configured and programmed processors, applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs) and digital signal processors (DSPs), for example.

Referring to FIG. 4B, software environment 1120 may be generally dividedinto two classes comprising system software 1121 and applicationsoftware 1122 as executed on one or more hardware environments 1110. Inone embodiment, the methods and processes disclosed here may beimplemented as system software 1121, application software 1122, or acombination thereof. System software 1121 may comprise control programs,such as an operating system (OS) or an information management system,that instruct one or more processors 1101 (e.g., microcontrollers) inthe hardware environment 1110 on how to function and processinformation. Application software 1122 may comprise but is not limitedto program code, data structures, firmware, resident software, microcodeor any other form of information or routine that may be read, analyzedor executed by a processor 1101.

In other words, application software 1122 may be implemented as programcode embedded in a computer program product in form of a computer-usableor computer readable storage medium that provides program code for useby, or in connection with, a computer or any instruction executionsystem. Moreover, application software 1122 may comprise one or morecomputer programs that are executed on top of system software 1121 afterbeing loaded from storage media 1106 into local memory 1102. In aclient-server architecture, application software 1122 may compriseclient software and server software. For example, in one embodiment,client software may be executed on a client computing system that isdistinct and separable from a server computing system on which serversoftware is executed.

Software environment 1120 may also comprise browser software 1126 foraccessing data available over local or remote computing networks.Further, software environment 1120 may comprise a user interface 1124(e.g., a graphical user interface (GUI)) for receiving user commands anddata. It is worthy to repeat that the hardware and softwarearchitectures and environments described above are for purposes ofexample. As such, one or more embodiments may be implemented over anytype of system architecture, functional or logical platform orprocessing environment.

It should also be understood that the logic code, programs, modules,processes, methods and the order in which the respective processes ofeach method are performed are purely exemplary. Depending onimplementation, the processes or any underlying sub-processes andmethods may be performed in any order or concurrently, unless indicatedotherwise in the present disclosure. Further, unless stated otherwisewith specificity, the definition of logic code within the context ofthis disclosure is not related or limited to any particular programminglanguage, and may comprise one or more modules that may be executed onone or more processors in distributed, non-distributed, single ormultiprocessing environments.

As will be appreciated by one skilled in the art, a software embodimentmay include firmware, resident software, micro-code, etc. Certaincomponents including software or hardware or combining software andhardware aspects may generally be referred to herein as a “circuit,”“module” or “system.” Furthermore, the subject matter disclosed may beimplemented as a computer program product embodied in one or morecomputer readable storage medium(s) having computer readable programcode embodied thereon. Any combination of one or more computer readablestorage medium(s) may be utilized. The computer readable storage mediummay be a computer readable signal medium or a computer readable storagemedium. A computer readable storage medium may be, for example, but notlimited to, an electronic, magnetic, optical, electromagnetic, infrared,or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing.

In the context of this document, a computer readable storage medium maybe any tangible medium that can contain, or store a program for use byor in connection with an instruction execution system, apparatus, ordevice. A computer readable signal medium may include a propagated datasignal with computer readable program code embodied therein, forexample, in baseband or as part of a carrier wave. Such a propagatedsignal may take any of a variety of forms, including, but not limitedto, electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable storage medium may betransmitted using any appropriate medium, including but not limited towireless, wireline, optical fiber cable, RF, etc., or any suitablecombination of the foregoing. Computer program code for carrying out thedisclosed operations may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages.

The program code may execute entirely on the user's computer, partly onthe user's computer, as a stand-alone software package, partly on theuser's computer and partly on a remote computer or entirely on theremote computer or server. In the latter scenario, the remote computermay be connected to the user's computer through any type of network,including a local area network (LAN) or a wide area network (WAN), orthe connection may be made to an external computer (for example, throughthe Internet using an Internet Service Provider).

Certain embodiments are disclosed with reference to flowchartillustrations and/or block diagrams of methods, apparatus (systems) andcomputer program products according to embodiments. It will beunderstood that each block of the flowchart illustrations and/or blockdiagrams, and combinations of blocks in the flowchart illustrationsand/or block diagrams, can be implemented by computer programinstructions. These computer program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

These computer program instructions may also be stored in a computerreadable storage medium that can direct a computer, other programmabledata processing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablestorage medium produce an article of manufacture including instructionswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments. In this regard, each block in the flowchart or blockdiagrams may represent a module, segment, or portion of code, whichcomprises one or more executable instructions for implementing thespecified logical function(s). It should also be noted that, in somealternative implementations, the functions noted in the block may occurout of the order noted in the figures.

For example, two blocks shown in succession may, in fact, be executedsubstantially concurrently, or the blocks may sometimes be executed inthe reverse order, depending upon the functionality involved. It willalso be noted that each block of the block diagrams and/or flowchartillustration, and combinations of blocks in the block diagrams and/orflowchart illustration, can be implemented by special purposehardware-based systems that perform the specified functions or acts, orcombinations of special purpose hardware and computer instructions.

The claimed subject matter has been provided here with reference to oneor more features or embodiments. Those skilled in the art will recognizeand appreciate that, despite of the detailed nature of the exemplaryembodiments provided here, changes and modifications may be applied tosaid embodiments without limiting or departing from the generallyintended scope. These and various other adaptations and combinations ofthe embodiments provided here are within the scope of the disclosedsubject matter as defined by the claims and their full set ofequivalents.

What is claimed is:
 1. A method for optimizing write operations to astorage device in a virtualized computing environment, the methodcomprising: monitoring write operations issued by an application runningon a virtual machine's (VM) operating system, wherein the VM is hostedby a hypervisor providing access to a storage device in a virtualizedcomputing environment; and causing a virtual file system (VFS) supportedby the operating system to call on a first para-virtualized file system(PVFS FE) supported by the operating system to execute a writeoperation, in response to determining that the write operation is towrite data to the storage device, wherein data that is to be written tothe storage device is first written to a VM memory area allocated to theVM and accessible to the hypervisor hosting the VM; wherein a secondpara-virtualized file system (PVFS BE) supported in the hypervisorasynchronously scans the VM memory to determine if any data that hasbeen stored in the VM memory is to be written to the storage device,wherein the asynchronous scanning is performed based on determining oneor both of: that a certain amount of data has been written to the VMmemory by the PVFS FE after a certain point in time; or that PVFS FE haswritten data to the VM memory a certain number of times after a certainpoint in time; and wherein the PVFS BE writes the data that is to bewritten to the storage device from VM memory to the storage device. 2.The method of claim 1, wherein the PVFS BE marks the data in VM memorythat is written to the storage device to indicate that said data hasbeen written to the storage device.
 3. The method of claim 1, whereinthe asynchronous scanning is performed in predetermined time intervalsbased on the expiration of a timing threshold.
 4. A system foroptimizing write operations to a storage device in a virtualizedcomputing environment, the system comprising: a processor for monitoringwrite operations issued by an application running on a virtual machine's(VM) operating system, wherein the VM is hosted by a hypervisorproviding access to a storage device in a virtualized computingenvironment; and the operating system causing a virtual file system(VFS) supported by the operating system to call on a firstpara-virtualized file system (PVFS FE) supported by the operating systemto execute a write operation, in response to determining that the writeoperation is to write data to the storage device, wherein data that isto be written to the storage device is first written to a VM memory areaallocated to the VM and accessible to the hypervisor hosting the VM;wherein a second para-virtualized file system (PVFS BE) supported in thehypervisor asynchronously scans the VM memory to determine if any datathat has been stored in the VM memory is to be written to the storagedevice, wherein the asynchronous scanning is performed based ondetermining one or both of: that a certain amount of data has beenwritten the VM memory by the PVFS FE after a certain point in time; orthat PVFS FE has written data to the VM memory a certain number of timesafter a certain point in time; and wherein the PVFS BE writes the datathat is to be written to the storage device from VM memory to thestorage device.
 5. The system of claim 4, wherein the PVFS BE marks thedata in VM memory that is copied to the storage device to indicate thatsaid data has been written to storage device.
 6. The system of claim 4,wherein the asynchronous scanning is performed in predetermined timeintervals based on the expiration of a timing threshold.
 7. A computerprogram product comprising a non-transitory computer readable storagemedium having a computer readable program, wherein the computer readableprogram when executed on a computer causes the computer to: monitorwrite operations issued by an application running on a virtual machine's(VM) operating system, wherein the VM is hosted by a hypervisorproviding access to a storage device in a virtualized computingenvironment; and cause a virtual file system (VFS) supported by theoperating system to call on a first para-virtualized file system (PVFSFE) supported by the operating system to execute a write operation, inresponse to determining that the write operation is to write data to thestorage device, wherein data that is to be written to the storage deviceis first written to a VM memory area allocated to the VM and accessibleto the hypervisor hosting the VM; wherein a second para-virtualized filesystem (PVFS BE) supported in the hypervisor asynchronously scans the VMmemory to determine if any data that has been stored in the VM memory isto be written to the storage device, wherein the asynchronous scanningis performed based on determining one or both of: that a certain amountof data has been written the VM memory by the PVFS FE after a certainpoint in time; or that PVFS FE has written data to the VM memory acertain number of times after a certain point in time; and wherein thePVFS BE writes the data that is to be written to the storage device fromVM memory to the storage device.
 8. The computer program product ofclaim 7, wherein the PVFS BE marks the data in VM memory that is copiedto the storage device to indicate that said data has been written to thestorage device.
 9. The computer program product of claim 7, wherein theasynchronous scanning is performed in predetermined time intervals basedon the expiration of a timing threshold.